1. Field of the Invention
The present invention relates to a semiconductor device having a circuit including a thin film transistor (hereinafter referred to as a TFT) and a manufacturing method thereof. For example, the invention relates to an electro-optical device typified by a liquid crystal display device having a liquid crystal display panel, a light emitting display panel including an organic light emitting element, or an electronic device on which an integrated circuit having an antenna is mounted as a part.
In this specification, a semiconductor device refers to all types of devices which can function by using semiconductor characteristics. An electro-optical device, a semiconductor circuit, and an electronic device are included in the category of all semiconductor devices.
2. Description of the Related Art
Recently, a technique of making a thin film transistor (TFT) using a semiconductor thin film (approximately, having a thickness of several nm to several hundreds nm) formed over a substrate having an insulating surface has been focused. The thin film transistor is widely applied to electronic devices such as ICs and an electro-optical device. Rapid development of a thin film transistor particularly as a switching element of an image display device is made.
Though various applications using such an image display device are expected, an application to portable devices is particularly focused. A glass substrate or a quartz substrate is currently used in many cases; however, there is a problem in that it is heavy and easily broken. In addition, a glass substrate and a quartz substrate are not suitable for mass production since they have a difficulty of being increased in size. Thus, formation of a TFT element over a flexible substrate, typically, over a flexible plastic film is tried.
However, since the plastic film has low heat resistance, maximum process temperature is required to be low. As a result, a TFT having more favorable electric characteristics than that in the case of forming a TFT over a glass substrate cannot be formed in the present situation. Accordingly, a liquid crystal display device or a light emitting element using a plastic film, which has high performance, is not realized.
At the situation, a technique is proposed, in which an element formed over a glass substrate is peeled from the substrate and transferred to another base material, for example, a plastic film or the like.
The present applicant (the assignee) proposes a peeling and transferring technique described in Reference 1 and Reference 2 (Reference 1: Japanese Patent Laid-Open No. H8-288522, and Reference 2: Japanese Patent Laid-Open No. H8-250745). In Reference 1, a technique in which a silicon oxide film to be a peeling layer is peeled by wet etching to be removed is described. In addition, a technique in which a silicon film to be a peeling layer is peeled by dry etching to be removed is described in Reference 2.
Further, the present applicant (the assignee) proposes a peeling and transferring technique described in Reference 3 (Reference 3: Japanese Patent Laid-Open No. 2003-174153). In Reference 3, a technique is described, in which, when a metal layer is formed over a substrate and an oxide layer is laminated thereover, a metal oxide layer of the metal layer is formed at an interface between the metal layer and the oxide layer and peeling is performed in a subsequent step by using the metal oxide layer.
In addition, the present applicant (the assignee) describes a technique in Reference 4, in which wind pressure of a gas blown from a nozzle in peeling, an ultrasonic wave, or the like is used (Reference 4: Japanese Patent Laid-Open No. 2003-163338).